1. Field of Invention
The present invention relates to modulators, and more particularly to further improvements in spread spectrum BPSK, or Binary Phase Shift Keying Modulation systems, the present invention contemplating a transmitter incorporating therein the utilization of an exclusive OR logic gate to replace an RF mixer stage, thereby providing enhanced gain at a lower energy consumption, with lesser cost and suppressed carrier output when compared to prior systems.
The present system teaches a new, superior, and less costly BPSK transmitter than taught or suggested by the prior art, providing a less complicated system while outputting increased gain over prior art modulator transmitters.
2. Prior Art & General Background
Prior to U.S. Pat. No. 5,265,120, spread spectrum BPSK modulators required conventional balance mixers to produce carrier suppression. These conventional modulators utilized either 1) a complex transistor array in conjunction with a transformer tunable with a potonciometer or 2) two center tapped transformers and four diodes, which arrangement required a high level drive circuit to modulate it, typically +7 to +15 dBM.
Besides the greater expense, increased complexity thereby contributing the probability of failure, and incompatibility with low power -10 dB CMOS logic drive circuitry, the prior art modulators typically produced on the order of six dB of signal loss, resulting in considerably less satisfactory overall performance when compared to the present invention.
The following patents were deemed to be of at least general pertinence to the present invention:
______________________________________ Patent Number Issue Date Inventor Class ______________________________________ 4,979,183 12/1990 Cowart 375-1 5,029,180 7/1991 Cowart 375-1 5,119,396 6/1992 Sanderford, Jr. 375-1 5,265,120 11/23/93 Sanderford, Jr. 375-1 ______________________________________
U.S. Pat. No. 5,265,120 teaches a prior BPSK spread spectrum transmitter which is compatible in sum respects with the present system. However, '120 does not contemplate the utilization of an exclusive OR logic gate to replace an RF mixer stage in the transmitter in the manner contemplated by the present invention, nor does '120 contemplate the features of FIGS. 5 or 6 of the present invention, nor the discussions relative thereto.
In the "General Summary Discussion of the Invention" section of '120, it was suggested that the '120 system could, in an alternative use, may be utilized as a frequency multiplier. For example, if the transistor, or its equivalent, is adequately fast, for example, F sub t&gt;1 GHZ, the system may be utilized to create at its output a higher frequency harmonic. However, this alternative system, to the extent disclosed, is believed wholly distinguishable from the present, applied for invention, which contemplates a scheme for a complete digital BPSK SS transmitter, and the logic of the modulator in '120 (shown in FIG. 2 of the present application) is clearly distinguishable from that contemplated in the present system, as illustrated in FIGS. 3 and 4 of the present application.
Further, '120 indicates that "it is a common radio design practice to utilize a non-linear device such as a diode, transistor, or the like to perform frequency multiplication. This is desirable because only lower frequency crystals are readily available, and as such, the lower frequency must then be translated into the higher, desired frequency. However, such systems are believed to be distinguishable from the present system, which provides enhanced performance with reduced cost, power consumption, and computational requirements". (Col 2, lines 18-25).
Nonetheless, the prior art has failed to contemplate a new and unique, lower cost BPSK transmitter utilizing an exclusive, in line OR logic gate to replace the RF modulator, or providing a transmitter incorporating a dual gate cascade to modulate the BPSK.